000
FXUS66 KSEW 180419
AFDSEW
Area Forecast Discussion
National Weather Service Seattle WA
930 PM PDT Thu Aug 17 2017
.SYNOPSIS...Seasonable summer weather will continue through
Friday with morning clouds and afternoon sunshine. A weak system
will brush the area Friday bringing slightly cooler conditions and a
chance of light rain or drizzle mainly to the north coast and north
Cascades. High pressure will begin to rebuild over the region Sunday
afternoon, reinforcing dry and warmer weather into early next week.
&&
.SHORT TERM...Onshore flow will bring stratus back to much of the
interior late tonight into early Friday morning. A weakening frontal
system will pass to the north of the area Friday resulting in a
slight
chance of light rain over the North Coast in the morning and over the
North Cascades during the afternoon. More than anything this feature
will likely bring little more than mid and high level clouds over
the northern half of the area Friday. Low clouds will return again
late Friday night into Saturday with afternoon clearing. Flow aloft
will remain westerly Saturday as the upper level ridge over the
Eastern Pacific remains slow to rebound. Temperatures should look
pretty similar to Friday with highs in the upper 60s to mid 70s over
parts of the interior.
.LONG TERM...The dirty ridge and zonal flow over the Eastern Pacific
will start to break down as an upper level trough digs into the Gulf
of Alaska from the Bering Sea Sunday. This will result in the upper
level ridge amplifying downstream of the approaching trough. Heights
will begin to rise over Western Washington Sunday afternoon through
Monday. Rising heights and warming aloft will help high temperatures
creep back up into the upper 70s to low 80s over the interior on
Monday and Tuesday with mostly sunny to sunny skies. The sky
forecast continues to look good for the eclipse on Monday. The ridge
axis will shift east Tuesday ahead of a weak upper level trough
approaching the region from the west. Medium range models continue
to differ on the timing and strength of this system hinting at a
chance of showers Wednesday afternoon into Thursday.
&&
.AVIATION...Westerly flow aloft through Friday with weak
disturbance moving by to the north Friday afternoon. Low level
onshore flow continuing through Friday.
Just some high clouds over the area this evening. Stratus is just
off the coast. Expect the lower stratus to be confined to the
coast and parts of the Southwest Interior Friday morning with the
somewhat weaker onshore flow Friday morning. Cloud deck out ahead
of weak system moving by to the north moving over Western
Washington in the morning with ceilings in the interior in the
4000-6000 foot range with the strato cumulus deck remaining over
the area into the evening hours.
KSEA...Just some high clouds tonight. Ceilings near 4000 feet
arriving at the terminal 12z-15z. Little change in the ceilings
through the evening hours. Light northwest winds this evening will
becoming light southerlies by 12z. Winds trying to come back
around to northwesterly late Friday afternoon. Felton
&&
.MARINE...A typical August pattern will prevail through the middle
of next
week. Expect onshore flow of varying strength to persist due to
higher pres offshore with lower pres east of the Cascades. A gale
watch is in effect Friday night for the central and eastern
Strait of Juan de Fuca with a slight increase in the onshore flow
behind the weak system going by to the north potentially
producing gale force westerlies. Felton
&&
.CLIMATE...Thursday was the 50th day in a row with a high of 70
degrees or more in Seattle. This is the 3rd longest streak on
record surpassed only by the 62 day streak from June 13 to August
13, 2015 and the 61 day streak from July 8 to Sept 6, 2003. The
last time Seattle had a high below 70 degrees was June 28 with a
high of 68 degrees. Felton
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Gale Watch from Friday evening through late Friday night for
Central U.S. Waters Strait Of Juan De Fuca-East Entrance
U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory until 5 AM PDT Friday for East Entrance
U.S. Waters Strait Of Juan De Fuca.
Small Craft Advisory until 6 PM PDT Friday for Central U.S.
Waters Strait Of Juan De Fuca.
&&
$$
www.weather.gov/seattle
You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html